Hey Barry - I was thinking - do you necessarily need a vapor barrier? That's mostly for the living area of houses where a lot of vapor is generated from things like cooking, showers, etc. You mentioned you have a furnace out there and some types of heat (depending on what you are calling a furnace) do generate vapor. If yours is a real furnace with proper venting to the outside, and is an occasional use device, I don't know that I'd really worry about vapor from combustion though. How humid does it get? If your exposed fiberglass does not get wet now, it's not going to get wet with any sort of covering over it. I'd leave the fiberglass in place. It does deaden sound somewhat - no a lot, but somewhat. It does keep your space at a somewhat more consistent temperature than without. I would cover it over with anything handy. Even sheet plastic if that's all I could get. I'd look around for rolls of burlap. It breathes, it's very durable. It won't cause a problem going over it when you finally decide to rock it. As far as your fire retardant factor is concerned, you need to look at your ceiling material to provide that. Most places are going to require 5/8in sheetrock in a garage space by fire code, but if this is not subject to that code, then 1/2 will likely be fine. You're not really going to gain any significant amount of fire retardant character out of any material that you just stretch across the joists and the insulation. It's all about heat and anything you stretch up there isn't going to present enough of a barrier to heat to amount to squat. That's why you need to think solid material... eventually.